The present invention relates to devices for loading and unloading trucks and similar motor vehicles. More particularly, the invention relates to a device of the type including a plurality of essentially endless, parallel conveyor cables which extend along a load platform of the truck and are movable relative thereto with respective upper conveyor passes projecting above the platform, a movable cross member fixed to the cables for moving them simultaneously, and a drive unit with chains for moving the cross member.
Loading and unloading devices of this type are known, for example, from U.S. Pat. Nos. 4,082,196 and 4,204,592. In these devices, the drive unit is constituted by a pair of hydraulic motors carried by the cross member and driving respective sprockets engaged by respective stationary chains the ends of which are fixed to the platform.
This solution involves a cross member of considerable structural complexity and appreciable size since it has to house the two hydraulic motors with their pumps, hydraulic reservoirs and valve units, and the load space available on the platform is thus reduced. Moreover, maintenance operations in the event of a breakdown of the drive unit may be extremely difficult when there is a load on the platform because of the resulting difficulty of access to the cross member. A further problem lies in the fact that the inevitable extension of the two chains may cause irregular movement or jamming of the cross member due, for example, to its misalignment from its correct position perpendicular to the length of the platform as a result of the differential extension of the two chains.
The object of the present invention is to avoid the aforesaid problems and to provide a loading and unloading device of the type defined above which is simpler and cheaper to produce and safer and more reliable in operation.